1. Field of the Invention
The present invention relates to a system for transformation of radiant energy from a remote energy source with an energy concentrating system. In particular, this invention relates to a method and design for collecting radiant energy from sunlight with a solar non-imaging concentrator to obtain optimum concentration for a given absorber shape.
2. Description of Prior Art
In the past, radiant energy concentrating devices have been used in space and on Earth to generate heat and electrical current from a light source such as the sun. However, because of the costs associated with capturing the sunlight in a widely useful form, solar energy has not approached its potential for becoming an important source of power. In particular, it is expensive in terms of capital cost to convert solar energy into electricity, substantially based on the complex manufacturing process involved in making efficient, high-precision solar concentrators with large apertures.
Systems are known for the generation of electrical power through the conversion of solar energy concentrated by a suitable refractor, such as a Fresnel lens, or a reflector, such as a parabolic dish system.
An approach is known where Fresnel lenses are used to collect and focus sunlight onto a photovoltaic array. These lenses are typically made of transparent acrylic sheets or optically clear silicone rubber materials. Glass materials can also be employed to provide structural strength of the design.
Despite the obvious advantages of the Fresnel lens, such as operational convenience due to forming the focal region on the concentrator""s back side, this approach still has no less obvious shortcomings.
The refraction index of plastic materials is essentially limited thus restricting concentration power and efficiency of the system. Prior art refractive lenses are generally bulky and fragile, complicating their manufacturing and use. The use of glass increases the weight, cost, and damage vulnerability of the lens. Furthermore, transparent refractive materials are known to degrade over time, due to interacting with chemicals and ultraviolet radiation.
Parabolic dish concentrators having much more concentrating power require extremely accurate continuous reflective surfaces of a very large aperture to achieve acceptably high concentration of the solar energy. Thus the prior art parabolic dish systems are expensive and heavy, due to the requirements of high optical accuracy. Continuous-surface parabolic mirrors are also not readily adaptable to provide a desired irradiance distribution for the receiver/absorber. However, the ability to provide a uniform concentration level is of a great importance for concentrating photovoltaic systems.
In the past, a lot of efforts have been made to improve the parabolic trough concentrators and lower the costs for a solar power system. One reflective concentrator that is especially designed for PV applications is disclosed in Jorgensen et al., U.S. Pat. No. 5,153,780, 1992. According to the patent, a dish reflector providing relatively uniform energy distribution on a PV array and consisting of a plurality of concentric concave reflective elements positioned along a reference parabolic dish surface is described. The solution, however, does not allow to achieve high concentration ratio attainable by conventional parabolic dishes. Furthermore, it has been a general disadvantage of all conventional retroreflecting devices that the operational convenience and use of larger absorbers/accessories or secondary concentrating optics disposed on the path of incoming energy are essentially limited due to unavoidable shadowing of the incident flux.
Vasylyev, in USSR Patent No. SU 1023270, issued Jan. 28, 1982, discloses the multi-element radiant energy concentrator xe2x80x9cPeresvetxe2x80x9d consisting of a set of ring-like reflectors, each reflector having the shape of a truncated circular paraboloid and sharing a common focal point. The xe2x80x9cPeresvetxe2x80x9d concentrator, however, is not adapted for achieving maximum energy concentration or providing a uniform energy distribution in the concentrated flux.
The present invention presents a novel solution particularly well suitable for achieving record concentration levels and energy conversion efficiency, as well as obtaining the desired illumination of an energy conversion unit.
In accordance with the present invention, the problems and shortcomings of the previously known systems are solved by a non-imaging system for radiant energy flux transformation comprising an energy concentrator incorporating a plurality of nested, ring-like reflective surfaces receiving the energy on the entrance aperture and focusing that energy to a receiver located on the side of exit aperture and disposed in energy receiving relation to at least one of said reflective surfaces.
Accordingly, one of the key objects and advantages of this invention is to provide improved energy collection and conversion system, said system uniquely combining Fresnel lens-like operation and dramatically improved concentration power and adaptability as compared to prior art systems. The invention can be essentially useful and greatly superior over conventional devices for solar energy applications by providing an improved device for converting the sunlight to heat and/or electricity so that the cost for use of solar energy is reduced.
According to one aspect of the invention, the non-imaging reflective surfaces of energy concentrator are designed and positioned to concentrate and direct the radiant energy toward a plurality of converging directions to form a common concentrated energy flux based on the superposition of concentrated energy fluxes reflected from individual reflective surfaces.
In accordance with another aspect of the invention, in a preferred embodiment, there is provided a reflective concentrator for collecting radiant energy in which reflective surfaces are designed and positioned to minimize screening and shadowing on other reflective surfaces.
According to yet another aspect of the invention there is provided an energy concentrator in which reflective surfaces have concave profiles represented by simple or compound segments of conical sections having parabolic, hyperbolic, circular, or elliptical shape. Furthermore, one or more reflective surfaces can be planar or have a profile represented by a set of straight lines approximating a curved shape. In addition, the profiles of reflective surfaces can be represented by segments of parametric curves or splines tailored to provide a desired illumination of the energy receiver.
Moreover, according to an embodiment of the invention, there is provided an energy concentrator in which one or more reflective surfaces is disposed in any one of a translated, a reversed and/or a rotated orientation relative to the others having the same basic arrangement.
According to further aspect of the invention, there is provided an energy receiver which can be used for receiving and converting the radiant energy to whatever useful type of energy. In particular, a receiver can be provided for collecting and converting sunlight to heat and/or electricity. The energy receiver can be a Stirling heat engine or an array of photovoltaic solar cells for generating electricity. Furthermore, the receiver can be associated with a secondary energy concentrator for further energy flux intensification or homogenization.
According to a still further aspect of the invention there is provided an energy flux transformation system further comprising at least one axle support for tracking the movement of the radiant energy source. Furthermore, the energy receiver can be mechanically separated from the energy concentrator.
Additional aspects, objects, and advantages of the present invention will be apparent to persons skilled in the art from a study of the following description and the accompanying drawings, which are hereby incorporated in and constitute a part of this specification.